Melt spinning of epsilon-polycaproamide filament



June 21, 1966 G. N. DULlN, JR

MELT SPINNING OF EPSILON-POLYCAPROAMIDE FILAMENT 2 Sheets-Sheet 1 Filed March 4 1963 INVENTOR GRADY N. DU l l N,JR.

ATTORNEY June 21, 1966 G. N. DULIN, JR

MELT SPINNING OF EPSILON-POLYCAPROAMIDE FILAMENT 2 Sheets-Sheet 2 Filed March 4, 1963 INVENTOR GRADY N. DU LIN JR.

ATTORNEY United States Patent 3,257,487 MELT SPENNING 0F EFSHLGN-POLYCAPROAMHDE FILAMENT Grady N. Dulin, in, Chester, Va., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New Yorlt Filed Mar. 4, 1963, Ser. No. 262,546 2 Claims. (Cl. 264176) This invention relates to the melt spinning of filaments from polycaproamide and more particularly to a novel method for improved production of polycaproamide yarn and removal therefrom of volatile impurities during melt spinning.

In the melt spinning of multifilament yarns from polycaproamide, it is generally found that the small amounts of residual e-caprolactam monomer contained by the polymer volatilize under the conditions of spinning. The volatilized lactam, during continuous spinning operation, accumulates and condenses as a liquid in the region neighboring the spinneret. Droplets of condensed liquid monomer which impinge upon the yarn in the spinning opperation cause localized weaknesses in the yarn which lead to increased frequency of yarn breaks during subsequent drawing and winding operations. Condensed liquid monomer which accumulates on the surfaces of critical apparatus elements of the spinning device cause malfunction of the spinning operation or necessitate frequent maintenance.

Generally suggested expedients for solving this problem include the use of aspiration means for continuously removing volatilized monomer from the region neighboring the spinneret. In view of the exacting requirements of a successful melt spinning process, the sacrifice of optimization of any parameter in order to accommodate a process innovation, e.g. an aspiration means, is generally detrimental to product or process results. A satisfactory aspiration means must therefore be carefully devised and critically combined with the other elements of the spinning apparatus to coact in the general functions and requirements of the spinning process. Otherwise aspiration means would be ineffective and could cause undesired effects upon the freshly extruded yarn structure due to improper thermal or mechanical factors.

It is an object of this invention to provide a novel method for the melt spinning of multifilament yarns of polycaproamide. It is another object of this invention to provide a melt spinning process utilizing apparatus having means for the efficient continuous removal of volatilized material from the vicinity of the spinneret without adversely affecting yarn quality or spinning process. It is a further object of this invention to provide a novel method for the continuous production of multifilament yarns of polycaproamide employing apparatus and process conditions which effectively remove volatilized monomer from the region of the spinneret without adversely affecting yarn quality or production efiiciency. These and other objects and advantages will appear hereinafter.

The objects of this invention are accomplished in general by utilizing a fiber-producing apparatus comprising a vertical spinning chamber; a horizontal multiorifice spinneret forming the top of said spinning chamber, and aspiration means around the upper end of said spinning chamber and in communication with said chamber via channels piercing the walls therebetween. Said aspiration means comprises a plenum and an exhaust port from which gas can be withdrawn. A pressure drop is imposed between spinning chamber and plenum atmosphere to create gas flow from the chamber through the channels, into and through the plenum, and out the exhaust port or ports. Within the spinning chamber and adjacent to the Patented June 21, 1966 inlet channels of the plenum, and preferably distant from the chamber axis at least about as far as the main wall sections of the chamber therebelow, is a vane which extends clear of the inner plenum wall and past said channels; preferably to points E where an angle of about 170 would be formed between the line drawn from E to the nearest point C of said channels, and the intersecting line from E to the point P which is on the axis of said spinning chamber'and is at the same horizontal level as said point C.

In my spinning process polycaproamide at a temperature in the range of 250 C. to 290 C. is extruded into contact with inert cooling gas or vapor in the spinning chamber at a jet velocity usually in the range between about 10 and about 40 yards per minute. A lower pressure is maintained in said plenum than in said chamber with a variation of pressure of less than 0.5 inch of mercury throughout the volume of said plenum, the flow rate of gas from the spinning chamber into and through said plenum being maintained between 1 and 20 cubic feet per minute and being at substantially equal volumetric flow rates through the successive areas of wall separating the spinning chamber from the plenum.

In a preferred embodiment of myinvention the cooling gas enters the spinning chamber through inlets in the walls thereof having a highest level at I below the plenum, so positioned with respect to the outermost spinneret orifice thereabove O, and the point P on the axis of the chamber at the level of the channels, that the angle OPT is 45 to In this embodiment a minor portion of the entering gas is drawn upward from the inlets, and the major portion of said entering gas flows downward in the spinning chamber below the inlets, cocurrently with the filaments, and exits below the inlets.

The invention will be more readily understood by reference to the following description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a sectional elevation of a spinning apparatus utilized in the process of the present invention taken along the vertical axis of the spinning chamber.

FIGURE 2 is a similarly taken sectional elevation of another embodiment of the spinning apparatus utilized in the process of this invention.

Referring now to the figures, in FIG. 1 a vertical spinning chamber is defined by cylindrical walls 1 and horizontal spinneret 2 having a multiplicity of orifices 3'. Aspiration means at the upper end of said spinning chamber comprises a plenum 4 surrounding the chamber and provided with an exhaust port 8 which leads to a vacuum pump or other suitable means, not shown, for withdrawing gas. As shown in FIG. 2, several exhaust ports 18, 18 can be provided instead of one port. Channels 5, forming a horizontal ring, communicate through the inner wall of the plenum 4 with the gaseous atmosphere of the spinning chamber. In FIG. 1, a vertical vane 6 within the spinning chamber is joined thereto along the full length of its upper edge by a horizontal lip 7, so that the vane covers but lies spaced inward from the channels 5. The vane extends clear of the inner plenum wall, and downward past the inlet channels of the plenum, and is at greater distance from the chamber axis than that of the main sections of the chamber walls therebelow. A representative point on the lower edge of vane 6, nearest to the channels, can be designated E. The position of E with respect to the nearest point C, of the channels and with respect to the point P, on the axis of the chamber and at the same level as the channels, is critical for optimum spinning characteristics of the apparatus. Whatever the form of the vane and its manner of connection to the spinning chamber walls, all points E must be located to bring the angles CEP into the range between 90 and It will be appreciated that when the channels lie at more than one level, there will be corresponding additional values of the angle CEP, as indicated at CE'P', C"EP of FIG. 2.

Inlet means 9 in the walls of the spinning chamber are provided for the entrance of cooling gas into the spinning chamber. Best results are generally obtained when the topmost of these inlets, which can be designated I, are in a critical area below the plenum, where the line IP drawn from I to P (designating, as before, the point on the axis of the chamber and at the same level as the inlet channels of the plenum) meets the line from P to O (designating the outermost of the spinneret orifices directly above I) at an angle of 45 to 120. Again when the channels lie at more than one level, there will be corresponding additional values of the angle OPI as indicated at O'PI', O'P"I' of FIG. 2.

Contact sealing means 10 of FIG. 1 are provided close below the plenum, comprising a lip 14 depending below the plenum and accommodated in horizontal groove 11, containing non-volatile inert liquid 15, such as molten Woods metal. An alternative as shown in FIG. 2 is to use a gasket 25, e.g. of the O-ring type or of soft or resilient material, in a groove 21 to make sealing contact between the w'alls of chamber 1(a) and plenum 4(a). These sealing means allow ready separation of the lower portion of the spinning chamber to give access to the spinneret and aspirator for maintenance routines.

At 12 in FIG. 1 an outlet is shown for cooling gas descending from inlets 9 toward the bottom of chamber 1. The form and position of this outlet is not critical provided it is at a point where the filaments 13 have solidified and cooled.

The plenum which surrounds the spinning chamber may be a single chamber or several separate chambers; each separate chamber requiring an individual exhaust port. The inner wall of the plenum constitutes the topmost wall of the spinning chamber. It is generally preferred. that the plenum be maintained at a sufficiently elevated temperature to further minimize the accumulation of condensable material therein.

The baffle or vane, preferably of non-porous, rigid construction, is adjacent to and spaced away from the channels in the plenum wall so as to block direct flow of gas from the immediately adjacent chamber atmosphere into said channels. Preferably the vane is supported along the full length of one edge or the other, as in the drawings; or alternately along first one edge, then the other. It can also be held just at a few points as a shield in front of the plenum channels. The sectional shape of the vane is not critical and may be angular or curved in various configurations provided however, it does not interfere with the yarn. The edges of the vane should preferably be continuous and uniform and lie in a single plane horizontal to the chamber and at distances from the channels to form angles CEP, as above defined, of 90--170.

The inlet channels to the plenum are preferably numerous holes of relatively small diameter roughly approximating their length. Usually they are circular, but narrow slits can be used. These channels are preferably dimensioned to create a pressure drop in the gas flowing therethrough, and maintain pressure differential of about 0.05 to about 10 inches of mercury between spinning chamber atmosphere and plenum. The plenum is so sized and the channels leading thereto and exhaust ports leading therefrom are so sized and spaced as to maintain this pressure differential substantially uniformly within about 0.5 inch mercury throughout the plenum volume, and maintain volumetric rates of gas flow which are substantially equal through all successive areas of the wall separating the spinning chamber and the plenum. For this purpose the plenum cross-sectional area suitably will exceed by several fold the total cross-sectional area of the inlet channels whereby the linear rates of flow of gas throughout the plenum will be a fraction of that through the channels. The channels can then be all of the same size and spaced uniformly and at a single level around the plenum and will then provide a uniform pressure throughout the plenum volume and equal volumetric rates and flow of gas into all areas around the plenum. The exhaust port or ports will usually be sized with a view to avoiding pressure gradients in the plenum; accordingly they will have relatively large cross-sectional area. Although usually the channels are evenly sized and spaced and all at the same level, they can be of different sizes and spacings and at different levels as long as equal volumetric gas fiow rates through each sizable area of the plenum are obtained.

In my spinning process, referring to FIG. 1, the freshly extruded filaments .13 emanating from orifices 3 undergo solidification starting in the region of the aspirator under the influence of a countercurrent flow of essentially inert gas or vapor entering through inlet means 9, said flow eing aminor part of the total flow of gas entering the chamber through the inlets 9. This flow of gas carries withit through channels 5 volatilized monomer given off by the molten freshly extruded filament in the upper regions of the spinning chamber. The filaments further solidify and cool in the lower part of the spinning chamber, below the inlets 9. The major portion of the entering inert gas fiows downwardly, cocurrent with the filaments, from inlets 9, and exits at a level where the filaments are cool, e.g. at outlet 12 at the bottom of the spinning chamber.

During the continuous operation inert gas is drawn into the inlets 9 and upwardly .at a rate of 1 to 20 cubic feet per minute, the rates used being greater for greater diameters of the spinning chamber; and thence through the channels 5; through the plenum 4; and out through exhaust port 8 to a vacuum pump, water aspirator or analogous means for propelling or transporting gas. Flow rates in excess of 20 cubic feet per minute are found to cause turbulence in the flow path of the freshly formed filaments in spinning chambers of usual commercial sizes, thereby causing the filaments to entangle or interadhere during their downward travel. Flow rates less than 1 cubic foot per minute are found inadequate in commercial size apparatus to prevent the accumulation of volatilized material in the upper regions of the spinning chamber. The major portion of the entering inert gas, up to say about percent thereof, descends in the spinning chamber cocurrent with the filaments and is withdrawn at the bottom of the spinning chamber. By thus splitting the flow gases into a minor upward, countercurrent flow in say the top one-third or less of the chamber and a major cocurrent flow in the remainder of the chamber, I find the volatiles can be removed from polycaproamide filaments; and they can be evenly cooled.

The function of my vane is apparently to create a relatively quiescent region of relatively dead air from which the exhaust is smoothly withdrawn; and to prevent cross currents of air being drawn from the immediate vicinity into the channels 5 of the plenum and creating turbulence. It should be appreciated that when an outlet for a major portion of the cooling air is provided below the inlets as in my preferred operations, it will require appreciable pressure differential between my plenum atmosphere and my spinning chamber atmosphere to draw a portion of the entering gas upward; and accordingly there will be a tendency to create local currents of air near the plenum. My vane contributes importantly to smoothing out operation under these conditions whereby uniformly high quality filaments are obtained in accordance with my invention.

The value of angle CEP made at the edges of the vane relates several geometrical factors: (a) the vertical position of the channels with respect to the edge of the vane, (b) the spacing of the vane with respect to the entrance to the channels, and (c) the diameter of the spinning chamber. It has been found that when this angle exceeds or is below about 90 the yarn quality is adversely affected.

The value of angle 0P1 relates the geometrical factors of: (a) vertical spacing of the outermost spinneret orifices and the uppermost gas inlet with respect to the avoided by the spinning apparatus of the present invention.

Their adverse efiects when they do occur, such as the sticking of filaments to each other or to the surface of the spinneret, can be minimized by providing a spinneret surface coating or lubricant, such as a film of liquid poly-organosiloxane. Thus, if turbulence, cross-fiow, or spinneret cooling should cause the molten polycaproamide extrudate to momentarily deviate onto or build up on an orifice, the liquid polyorgan-osiloxane will minimize the tendency of the polymer to adhere to the metallic spinneret surface.

In order to provide for periodic inspection and maintenance of the spinneret and associated aspirator means and restoration of polyorganosiloxane which may be employed on the spinneret, it is desirable to employ coupling means associated with the chamber wall to facilitate repeated dismantling and reassembly of the spinning apparatus. Said coupling means may preferably be located below the aspirator means, although in some embodiments the coupling means may desirably be positioned above the aspirator means. The coupling means must provide an efiective airtight .seal so as to prevent extraneous air from entering the spinning chamber. Preferred coupling means should thus include a deformable, resilient member which can conform to the geometrical requirements of the two coupling entities, thereby providing a rapid-acting, tight seal which will retain its efiectiveness even after many coupling cycles. Specific resilient members include elastorneric O-rings, impregnated gaskets, and troughs of non-volatile liquids or molten metal into which one of the coupling members becomes immersed to form an airtight seal.

The orifice of the spinneret may be circular or polygonal, having symmetrical or asymmetrical configuration, or may consist of separate groups of closely spaced orifices whose combined extrudate merges partially or entirely to form a single integral filament. Filaments produced from said orifices will generally have a crosssectional configuration determined by the orifice and may be round, angular, multilobal, multibranched, crenulated, dog-boned or the like.

The following example describes completely a specific embodiment of my invention illustrative of the best mode contemplated by me of carrying out my invention; but it is not intended to restrict the invention to all details of the example.

Example Employing a spinning apparatus essentially as represented by FIG. 1, a polycaproamide polymer having a formic acid relative viscosity of 45 (as determined by ASTM procedure D78953T) and volatiles content of about 1%3% by weight, was extruded at a temperature of 262 C. and at a jet velocity of about yards per minute through a stainless steel spinneret containing 136 orifices each of 0.018 inch diameter, radially arranged. The spinneret face had been wiped with a liquid polyorganosiloxane before spinning commenced. The spinning chamber into which the filaments were extruded was about 22 feet long and 9 inches in diameter. It was supplied with 41 cubic feet per minute of air at 82 F. entering through a layer of felt to equalize pressures, then through inlet ports 9, starting at level I about 8 inches 6 below the spinneret. The angle OPI was 83. The inner plenum wall as shown in FIG. 1 was pierced by circular channels each about li inch in diameter and inch long, uniformly set in a ring around the axis of the chamber. The diameter across this ring was about 1 foot.

The vertical, downwardly extending vane 6 was at a distance of about /41 inch from the inner plenum wall and the channels therein. It was positioned so that angle CEP was 129. A pressure differential as against the atmosphere of the spinning chamber of 0.6 inch of mercury was maintained throughout the volume of plenum 4 by means of a vacuum pump acting through a condenser for recovery of monomer and communicating with the plenum through a single exhaust port. The volumetric flow rate through the plenum to the exhaust pump was 8 cubic feet per minute, the remainder of the air exiting at the bottom of the chamber where the filament emerged.

During continued spinning little condensed monomer was observed to form on equipment surfaces in the region of the spinneret. The yarn bundle remained unaltected by the action of the aspirator means, and the surface of the spinneret retained constant desired temperature.

In a comparative test for the purpose of determining the effect of the spinning process of this invention on yarn quality the spinning apparatus of this example was operated to produce large samples of yarn, first with the aspirator functioning and then with the aspirator turned olf, all other factors being identical. The yarn emanating from the bottom of the spinning chamber was in each case drawn at a draw ratio of 4.4:1, thereby producing a yarn of 839 denier. During the drawing, winding and twistingof each of the two yarn products in the production of spooled yarn of marketable quality, there was recorded the number of defects such as breaks of the yarn and occurrences of wraps of stripped-out filaments on rolls. The results obtained were as fol- The overall decrease in yarn defects in the test wherein the aspirator was used led to an increased yield of acceptable quality yarn of greater than 7 percent. The test run wherein the aspirator was not used moreover required relatively frequent disassembly in order to clean the surfaces in the upper region of the spinning chamber.

I claim:

1. Process for production of improved epsilonpolycaproamide filaments which comprises extruding a multiplicity of molten polycaproamide filaments through a spinneret downwardly into a confined zone to which inert gaseous fluid is admitted, a minor portion of said gaseous fluid being drawn upward in said confined zone from its point of admission and the major portion of said gaseous fluid flowing downward in said confined zone below its point of admission, said upwardly drawn minor portion being drawn into an exhaust zone around the top of said above mentioned confined zone at a rate between about 1 and about 20 cubic feet per minute from said confined zone and at substantially uniform pressure differential and substantially equal volumetric flow rates through the successive areas separating the exhaust zone from the confined zone containing the filaments; a relatively quiescent region being maintained in the gaseous fiuid in the confined zone in the vicinity of the spin- 7 neret and exhaust zone by a bafile or vane blocking off direot flow of gas from the zone immediately below the spinneret into the exhaust zone, but leaving these zones in communication around the lower edge of said bafile; said molten filaments being solidified under the influence of the upwardly drawn gaseous fluid and by the cooling action of the downwardly flowing gaseous fluid; said upwardly drawn fluid serving to carry away to the exhaust zone, volatilized monomer from the polycaproamide filaments; the zone of admission of the gas being within the upper one-third of the said confined zone and being below said exhaust zone and the lower edge of said bafile.

2. Process of claim 1 wherein said quiescent region is at substantially the same pressure as the atmosphere of said confined zone, and said exhaust zone is maintained at substantially constant pressure which is lower than the pressure in said confined zone by about 0.0'5-10 inches of mercury; the temperature at said exhaust zone being maintained above the dew point of monomer vapors.

References Cited by the Examiner UNITED STATES PATENTS 2,217,743 10/1940 Greenewalt 18-8 2,252,684 8/1941 Babcock 188 2,719,776 10/1955 Kummel 264l76 2,847,704 8/1958 Scheers 264l76 2,957,747 10/1960 Bowling l854 3,015,480 l/1962 Nawrath et al 18-8 3,079,219 2/19 63 King 185'4 FOREIGN PATENTS 166,476 10/1953 Australia. 714,330 8/1954 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

C. B. HAMBURG, Examiner.

K. W. VERNON, Assistant Examiner. 

1. PROCESS FOR PRODUCTION OF IMPROVED EPSILONPOLYCAPROAMIDE FILAMENTS WHICH COMPRISES EXTRUDING A MULTIPLICITY OF MOLTEN POLYCAPROAMIDE FILAMENTS THROUGH A SPINNERET DOWNWARDLY INTO A CONFINED ZONE TO WHICH INERT GASEOUS FLUID IS ADMITTED, A MINOR PORTION OF SAID GASEOUS FLUID BEING DRAWN UPWARD IN SAID CONFINED ZONE FROM ITS POINT OF ADMISSION AND THE MAJOR PORTION OF SAID GASEOUS FLUID FLOWING DOWNWARD IN SAID CONFINED ZONE BELOW ITS POINT OF ADMISSION, SAID UPWARDLY DRAWN MINOR PORTION BEING DRAWN INTO AN EXHAUST ZONE AROUND THE TOP OF SAID ABOVE MENTIONED CONFINED ZONE AT A RATE BETWEEN ABOUT 1 AND ABOUT 20 CUBIC FEET PER MINUTE FROM SAID CONFINED ZONE AND AT SUBSTANTIALLY UNIFORM PRESSURE DIFFERENTIAL AND SUBSTANTIALLY EQUAL VOLUMETRIC FLOW RATES THROUGH THE SUCCESSIVE AREAS SEPARATING THE EXHAUST ZONE FROM THE CONFINED ZONE CONTAINING THE FILAMENTS; A RELATIVELY QUIESCENT REGION BEING MAINTAINED IN THE GASEOUS FLUID IN THE CONFINED ZONE IN THE VICINITY OF THE SPINNERET AND EXHAUST ZONE BY A BAFFLE OR VANE BLOCKING OFF DIRECT FLOW OF GAS FROM THE ZONE IMMEDIATELY BELOW THE SPINNERET INTO THE EXHAUST ZONE, BUT LEAVING THESE ZONES IN COMMUNICATION AROUND THE LOWER EDGE OF SAID BAFFLE; SAID MOLTEN FILAMENTS BEING SOLIDIFIED UNDER THE INFLUENCE OF THE UPWARDLY DRAWN GASEOUS FLUID AND BY THE COOLING ACTION OF THE DOWNWARDLY FLOWING GASEOUS FLUID; SAID UPWARDLY DRAWN FLUID SERVING TO CARRY AWAY TO THE EXHAUST ZONE, VOLATILIZED MONOMER FROM THE POLYCAPROAMIDE FILAMENTS; THE ZONE OF ADMISSION OF THE GAS BEING WITHIN THE UPPER ONE-THIRD OF THE SAID CONFINED ZONE AND BEING BELOW SAID EXHAUST ZONE AND THE LOWER EDGE OF SAID BAFFLE. 